The present invention relates to SiAION material compositions particularly useful for machining of heat resistant alloys.
Heat resistant alloys are generally machined at very low cutting speeds when using cemented carbide tools due to the very low machinability of heat resistant alloys in comparison to cast iron and steel. More recently developed ceramic cutting tool materials like SiAION (U.S. Pat. No. 4,711,644, U.S. Pat. No. 4,818,635 and U.S. Pat. No. 5,370,716) or silicon carbide whisker reinforced alumina tools (U.S. Pat. No. 4,789,277 and U.S. Pat. No. 4,961,757) have significantly increased the productivity by permitting much higher cutting speeds than can be utilized when using cemented carbide tools. Silicon carbide whisker reinforced alumina tools can normally be used at higher cutting speeds than SiAION tools due to a better chemical stability whereas SiAION tools can be used at higher feed rates due to a better toughness behavior. Commercial SiAION ceramic cutting tools either are pure beta SiAION (Si.sub.6 --.sub.z Al.sub.z O.sub.z N.sub.8-Z) where O&lt;z&lt;3 and intergranular phases, or beta plus alpha SiAION [(Si,Al).sub.12 M.sub.x (O,N).sub.16 where x is between 0.1 and 2 and M can be Li, Ca, Mg, Hf, Zr, Ce, Y, Sc or other lanthanides] and intergranular phases.
U.S. Pat. No. 4,818,635 discloses a SiAION material, where the presence of polytype of SiAION together with beta and/or alpha SiAION constitutes the main components.
U.S. Pat. No. 5,370,716 claims a ceramic metal cutting material consisting of SiAION grains and an intergranular phase. Preferably 70% of the SiAION grains consist of beta SiAION, Si.sub.6 --.sub.z Al.sub.z O.sub.z N.sub.8-z, with z values between 1.5 and 3.